The present invention relates to a new and improved method for the detection of short-circuits on lines operated with voltages and currents containing an alternating component, by determining the course as a function of time of the voltage and current at a measurement location in the form of measurement voltages and measurement currents. Further, the invention relates to apparatus for the performance of such method.
The detection of short-circuits on lines is a prerequisite for carrying out subsequent protective measures and therefore as the stimulus for a fault location or fault location-localization at a sufficiently limited line section plays a major role in the design of a line- or network protective system. In consideration of the extremely different possibilities of fault location or fault location-localization and furthermore the identification of the type of fault (selection) following the fault detection the latter constitutes an independent technical problem which generally also can be solved with its own circuit devices.
Normally fault detection takes place for instance with the aid of a minimum-impedance method and appropriate relay, as for instance has been disclosed in the publication "Brown Boveri Mitteilungen", Volume 53, No. 11/12, pg. 788. Such type methods are predicated upon a comparison of current and voltage, in other words respond to the current increase characteristic of a short-circuit accompanied by a rather pronounced dropping of the line voltage at the measurement location. The method which has been indicated to be known to the art functions with rectification of signals associated with the measurement voltage and measurement current and with a difference formation of the rectified signals. The null cross-overs of the difference signal determine the integration interval of a subsequent integration with constant ascending speeds. The momentarily obtained amplitude of the time integral is therefore a function of the relationship between the measurement voltage and measurement current, so that the relationship prevailing in the case of a short-circuit can be associated with a predetermined boundary value of the time integral, and upon falling below or exceeding this boundary value there can be determined the normal state or fault state, respectively, of the line.
With the comparatively rapid excitation method and excitation apparatuses of the type known, to which there also belongs the above-mentioned example, there can be realized detection times, which desirably should be further reduced in the interest of more rapidly undertaking protective measures.